Presently, the design of centrifugal separators is primarily adapted to a liquid-solids mixture introduced tangentially at high velocity into the base of an inverted cone-like vessel so that the heavier solids are centrifugally forced outwardly toward the wall of the retaining vessel and flow by gravity toward the apex of the inverted cone, exiting the apex with a metered amount of liquid through an aperture called the underflow. The remaining liquid containing the lighter solids called the overflow flows upwardly from the center of the cone through a hollow tube outlet called the vortex finder. Devices of this type are described in the article "Wet Cyclones," Chemical Engineering (June 1955).
Such prior art designs are limited in the volume capable of being efficiently treated in the separator due to the physical phenomenon that increasing the size of the separating vessel to obtain adequate time for efficient separation reduces the circular velocity and, hence, the centrifugal force required to obtain efficient separation. Accordingly, a multiplicity of small volume separators are frequently used in tandem to accommodate a larger volume where a high degree of separation is required, and to avoid the high velocities and resultant power requirements necessary in larger separators to effect the same degree of separation.
U.S. Pat. No. 3,754,658 is a pulp thickener relying upon a pressurized dewatering mechanism.
Another limitation in the design of prior art centrifugal separators is the length of time that solids in a liquid-solids mixture entering such a separator are subjected to centrifugal force generated by the circular flow. In most applications, this length of time is a minute fraction of a second.
Another inherent difficulty in the design of present centrifugal separators is in determining the size and proper placement of the appropriately named vortex finder in order to provide efficient separation, since these factors vary with the inlet velocity, internal pressure, and ratio of the liquid to solid density.
A further disadvantage of present centrifugal separators is the extreme wear on certain elements of the separators subjected to heavy abrasion due to the high velocities required to effect meaningful separation in the short time a liquid-solids mixture is in the separator.